The invention relates to superconducting rotating machines (e.g., a superconducting electric generator or motor) and their constructions.
The worldwide demand for additional electrical generation is ever increasing. To meet these demands, larger and more efficient electrical generators are being developed. Electric generators convert rotational mechanical input energy (e.g., that from a steam or gas turbine) into electricity by rotating a rotor field within stationary armature conductors. In conventional generators, the generator field is produced with copper windings or permanent magnets.
The overall efficiency of an electrical generator is affected by the losses in the rotor windings and in the armature windings. By using superconducting wire for the field windings, these losses become almost negligible. Moreover, the overall volume of an electrical generator using high temperature superconductor (HTS) generator can be as much as ⅓ the volume of its conventional equivalent.
Such superconducting generators are also finding application in power plants where expansion is difficult (e.g., shipboard or locomotive power). Smaller, lighter HTS generators use an xe2x80x9cair corexe2x80x9d design, eliminating much of the structural and magnetic steel of a conventional equivalent. Construction, shipping, and installation are all simplified and less costly.
The invention features a superconducting rotating machine which produces increased electric power with significantly lower losses while being smaller and lighter than conventional equivalent electric rotating machines.
In a general aspect of the invention, the superconducting rotating machine includes a direct current field excitation source and an alternating current armature winding mounted on a static support member, at least one of the excitation winding and armature including a superconducting material, a core member formed of a magnetic permeable material and rotatable around the static support member, and a refrigerator unit which cryogenically cools at least one of the excitation winding and armature.
In the above arrangement, the field excitation source and armature winding are mounted statically to a support member and the core is rotated about the field excitation source and armature winding. This arrangement has numerous advantages. Specifically, because the field excitation source and armature winding are not mounted on a rotating, or otherwise moving member, difficulties associated with cooling moving parts are eliminated. Thus, either or both of the field excitation source and armature winding can be more easily cooled, for example, with a cryocooler. Because cooling is easier, either or both of the field excitation source and armature winding, can be formed of superconducting material. This advantage is important because a significant amount of the total electrical losses in an electric rotating machine are associated with the field excitation source and armature winding. Further, because the electrical losses, weight, and volume of the rotating machine are significantly reduced, the overall efficiency and reliability of the machine is increased. Moreover, installation, as well as retrofitting, of this construction is simplified and less costly.
Embodiments of this aspect of the invention may include one or more of the following features.
For example, in one embodiment, the field excitation source is a non-superconducting permanent magnet, with the armature winding including the superconducting material. Alternatively, the field excitation source is in the form of a coil (superconducting or non-superconducting).
The superconducting material is a high temperature superconductor (HTS) and may be in the form of a tape having a thickness and a width greater than the thickness. In embodiments utilizing HTS tape, the field excitation source is a pancake coil, and preferably a double pancake coil. The double pancake coil is preferably a saddle-shaped racetrack coil. Because HTS materials are typically ceramic-based (e.g., BSCCO), such materials are intrinsically less flexible. The saddle-shaped racetrack configuration is well-suited for providing pancake coils with a shape which conforms to rounded support structures.
The superconducting rotating machine may include a plurality of field excitation sources, circumferentially spaced from each other and mounted on the static support member. In preferred embodiments, adjacent ones of the excitation sources have polarities of opposite sense. Thus, when the core member rotates past the excitation sources, the alternating polarity of the magnetic flux causes an AC voltage to be generated.
The core member includes salient members extending in a direction substantially parallel to the longitudinal axis. The salient members, in essence, are extended portions of the core member closely spaced from the excitation winding and armature. First and second groups of salient members are spaced from the longitudinal axis of the core member by first and second radial distances, respectively, with the second radial distance being greater than the first radial distance. This arrangement provides a pair of salient poles between which armature and excitation winding pass, thereby ensuring a good magnetic flux path. The core member is in the form of a radially-stacked lamination of the magnetic permeable material to reduce lossy eddy currents.
In another aspect of the invention, a polyphase rotating machine (e.g., three-phase machine) includes a plurality of direct current excitation source groups and a plurality of alternating current armature windings. Each armature winding associated with and magnetically coupled to a corresponding one of the plurality of excitation source groups. Each excitation source group is mounted on the static support member and has at least one excitation source including a superconducting material. Each excitation source from a first one of the excitation source groups is radially spaced from an excitation source of a second one of the excitation source groups. The polyphase rotating machine also includes a core member formed of a magnetic permeable material and rotatable about a longitudinal axis and around the static support member, as well as a refrigerator unit which cryogenically cools the excitation windings. The core member is disposed adjacent to the excitation windings of the phase winding groups and armature windings.
Embodiments of the polyphase rotating machine may include one or more of the features described above as well as the following additional feature. The core member includes salient member groups, each group extending in a direction substantially parallel to the longitudinal axis and radially spaced from another of the groups of salient members, each of the phase winding groups positioned between the groups of salient members. This arrangement provides salient members on either side of each excitation source and armature winding.
Other advantages and features of the invention will become apparent from the following description and claims.